'When I was wearing the headset, I would start shouting because I did not realize how well it was working...' Aaron Kapaldo (EE '03)

Fall 2003

A Quieter Headset, Nearly Perfect Results

A senior design team made a headset quieter and achieved an almost perfect match between prototype and simulation. Clockwise: Joe Stinnet (wearing the headset), Nathan Pagel, Aaron Kapaldo, and Ryan Hurrell.

A senior EE design team not only made a headset quieter last semester, but also produced results almost identical to the initial computer simulation of the design. It worked perfectly the first time it was tested.

Joe Stinnet, Ryan Hurrell, Nathan Pagel, and Aaron Kapaldo designed a controller to improve a pair of noise canceling headphones as a class project for ECE 4406, Control Systems II, taught by William Baumann.

Reverse EngineeringTheir charge was some reverse engineering, then making the headset quieter.

First they were to analyze the headset to determine the performance of the system, and the nature and transfer function of the controller and plant. Then they designed and implemented a controller that achieved better performance in terms of rejection, spillover, and robustness.

"When we implemented the design we had developed on the computer, it worked," Stinnet said. "That was a surprise. I never expected it to work the first time...Our results were almost identical to the simulated results on the computer." He explained that the team had taken extra precautions, such as several iterations and simulations, to make sure the design matched the theory.

Relentless Measuring Yields SuccessThe group attributed their success to "relentless measuring" and their simulations. "We spent most of the time measuring," Hurrell explained. "When we thought we were close enough and could account for any discrepancy, Dr. Baumann would suggest another method of measuring. Each time we thought we had made our final measurement and could head to the design phase, we'd be back two days later taking it apart and measuring again," he said.

The small scale of the circuit and the large size of the equipment made accurate measurements a challenge, he said.

"It was worth it," Kapaldo said. "Our design was so exact because of this. The two weeks we took to make sure the theory and design was correct was more valuable than four weeks of putting it together again and again," he added.

Noise Suppression vs. High Frequency SpilloverThe most significant design challenge involved finding a good balance between noise suppression and spillover. "We had to find the best trade-off point between suppressing the low frequency noise and the resulting spillover in high frequency," Stinnet explained. "We don't know how much high frequency a person's ears can handle before it creates a problem. Also, if you are listening to the headphone and hear annoying high frequency, you will not enjoy wearing it."

Kapaldo enjoyed wearing the headphones. "It was a great feeling to put them on and barely hear outside noise. When I was wearing the headset, I would start shouting because I did not realize how well it was working," he said.

"When I look back, this will be the most valuable thing I did in college," said Pagel.